The initial push to get me in to Elixir was indeed its performance, but that’s not what kept me. At the same time, I also tried learning Go and more recently, Rust has caught my attention.

In most cases, languages like Go and Rust can push more raw performance out of a simple “Hello World” benchmark test — exactly what I initially did to compare Ruby on Rails to Elixir / Phoenix. The more I used Elixir, the more I gained an appreciation for what I now regard critical language features (yes, most of these apply to Erlang and other functional languages too).

Immutability

This is a big one. Manipulating a mutable data structure is essentially changing the data in memory directly. This, however, is susceptible to the classic race condition bug programmers encounter when writing multithreaded programs:

Thread 1 reads “1” from “a”

Thread 2 reads “1” from “a”

T1 increments “1” to “2” and writes it to “a”

T2 increments “1” to “2” and writes it to “a”

In this case, the intended value is “3” because the programmer incremented “a” two times, but the actual value in memory is “2” due to the race condition.

In systems with immutable variables, this class of bug doesn’t exist. It forces the programmer to be explicit about shared state.

Lightweight Processes

A typical Erlang (Elixir) node can have millions of processes running on it. No, these are not your traditional OS processes — they are not threads, either. The Erlang VM uses its own scheduler and thread pool to execute code. The memory overhead of a single process is usually very light — on my machine, it’s 2.6kb (SMP and HiPE enabled).

Inter-Process Communication

Another big one.

Want to send a message to another process?

send(pid, :hello)

Want to handle a message from another process?

receive do
:hello -> puts "I received :hello"
end

This works on processes that are running in the current node — but it also works across nodes. The syntax is exactly the same. The “pid” variable in the example is able to refer to a process anywhere in the cluster of nodes. The other node doesn’t even have to be Erlang, it just needs to be able to speak the same language, the distribution protocol and the external term format.

OTP

You can’t talk about Erlang or Elixir without bringing up OTP. OTP stands for “Open Telecom Platform” (Erlang was initially developed by Ericsson for use in telecom systems). OTP is a framework with many battle-tested tools to help you build your application — for example,

OTP is, for all intents and purposes, part of the Erlang standard library. Thus, it is automatically included in any Elixir application as well. The nuts and bolts of OTP are out of the scope of this blog post, but having such a rich toolbox is like a breath of fresh air coming from Ruby (I thought the same when switching full-time from PHP to Ruby).

Conclusion

I’ve learned a lot in this past year, and yet I feel like I’ve only scratched the surface. Thanks for reading!

There’s a guide to writing browser acceptance tests for Phoenix. Acceptance tests are nice, but sometimes you want to have unit tests. This is very easy to do with your Elixir code, but what about your JavaScript code that lives inside your Phoenix application?

I couldn’t find a good guide on this, so I’ll go over what I have set up for one of my latest Phoenix projects.

Setup

First, install mocha if you haven’t already. I’ll be using mocha, but you can use whatever test runner you want to. You’ll also need babel-register — this will allow you to use Babel while the tests are being run in Node.

Set up mocha to run your tests in package.json. The default Phoenix & Brunch installation doesn’t include a “scripts” section, so you’ll probably have to create it. If it’s already there, just add the “test” line.

Now, set up Babel to pick up the default preset (if you’re setting a different preset in your brunch-config.js, you just replace es2015 with what you have there). Put this in .babelrc in the root directory of your project.

{
"presets": ["es2015"]
}

Now, you can put JavaScript unit tests in test/js and by running npm test, they will run inside Node.

Note that npm test will not be automatically run when you run mix test, so you’ll have to change the way tests are run on your CI run by either changing the test command to mix test && npm test or adding the npm test command to your CI configuration.

Example Test

Say we have a module that does nothing but export a function that returns the string "something":

In Ruby, there is a very handy class called StringIO. Basically, it allows you to treat a string like you would an IO object, such as an open file, etc. Very useful for in-memory “files” that you may not want to write to a temporary file.

In Elixir, there is a module called StringIO in the standard library. At first glance, these seem pretty similar:

Ruby:

Pseudo I/O on String object.

Elixir:

This module provides an IO device that wraps a string.

However, there are some subtle differences. For example, you can’t rewind the position of an Elixir StringIO:

Note that because of differences between Elixir’s IO / File modules and Erlang’s file module (probably related to how Elixir works with character encodings), you have to use the binary option to :file.open/2 and the bin-prefixed functions in Elixir land.

As a small side project, I recently launched a “link unroller” service. This is a very simple service. You give it a URI, and it follows any redirect chain for you. Then it spits out the final URI via a friendly JSON API.